a(n) = Bell(n)*(2 - 0^n).

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =30a(5) =104a(6) =406a(7) =1754a(8) =8280a(9) =42294a(10) =231950a(11) =1357140a(12) =8427194a(13) =55288874a(14) =381798644a(15) =2765917090a(16) =20960284294a(17) =165729739608